Manufacture of safety explosives



g terial of stiff, paper cartridge containe Patented Apr. 27, 1937 UNITED STATES MANUFACTURE, or smart EXPLOSIVES James Sinton Bruce Fleming,

Sootland, asslgnor. to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application March 1a, 1934, Serial m 715,301. In (treat Britain .March 14.

'13 cla ms. (01. 102-6) This invention relates to safety explosives of the type in which the explosive charge is provided with an annulus, sheath, covering or casing comprising one or more flame-quenching and 5 cooling materials, hereinafter referred to collectively as cooling materials;

. Among the methods previously proposed for 1 sheathing or encasing the explosive in cooling material there may be mentionedi-(l) loading the cooling. material into a paper jacket surrounding the cartridge, the jacket being formed by a suitable arrangement. of the wrapping paper;

(2) forming the cooling material, together with a binding agent such as plaster of Paris, into a jacket surrounding the explosive charge and then treating it with water; and (3) casting or mould- ,ing the cooling material into the required annular shape for surrounding the explosive charge. It has also been proposed to impregnate the ma: rs with solutions of cooling materials and to dry the i product. Y

According to the present invention, I surround, sheath, cover or encase the explosive in a- Jacket, consisting of fibre bondedv cooling mate-' rial in flexible sheet form, prepared by mixing a loose fibrous pulp with an aqueous suspension of one or more cooling materials, draining the solid mixture to form a felt, and drying the felt so that so it maybe handled without'damage.

The fibrous pulp/which I use may be a cellulose pulp, or carded or pulped cotton textiles, or

asbestos fibre material, kraft pulp is a particu larly suitable material. The essential property of the Pulp usedjs that the fibres should not be felted or compressed together, but. should be in loose form. Thus, if 'the raw material is in board form, it must be disintegrated and pulped. Subject to this requirement practically any 40 fibrous material maybe-used. I prefer, however, to use a cellulose pulp in which the fibres are not all the same length. I prefer that the cellulosic fibres should have undergone a beating process designed to cause "fibrlllation, i. e. teasing out of the ends of theflbres; as I find that the tensile strength of thebonded material subsequently made fromthese fibres is thereby greatly enhanced.

The invention is applicable to the ordinary cooling materials for explosives, such as calcium fluoride, sodium fluoride, sodium chloride, or sodium bicarbonate, or a mixture of two or more of such salts; deliquescent materials, however, are unsuitable. The amount of fibre may be as low as 2%. by weight of the-dry weight of the 5 fibre bond'ed cooling material, but preferably amounts ofabout 440% are used.

In the case of cooling materials which are insoluble in water; water is a suitable medium in which to mix the fibres'with the cooling mate- 10 rials; and in the case of Water-soluble materials I may use an aqueous solution previously saturated with respect to the soluble materials.

In carrying out. my invention, 1 mixthe.

fibres (which may be in the water-wet state) and 151 the cooling materials in the liquid medium with liquid medium isremoved as muchas possible, for 20 instance by pressing or suction. The damp felt is then dried at a slightly raised temperature,

- for example 40 C. when the solubility of the salts used does not greatly increase with rise of temperature, a higher'drying temperature may 25 be used. From 1 to 5% of moisture may conveniently be left in the materiaL In order to prevent loss'of flexibility-by undue evaporation from the material, Imay add to the composition small quantities of a non-volatile hygroscopic 30 substance compatible with the other constituentsof'the mixture, such as glycerine. However, this is not usually necessary.

' I then wrap the explosive cartridge, which is preferably already wrapped in'paper, within 'a 35 sheet of the dried felt. The-join may be made with gum, or other adhesives. An outer wrapping of paper may be applied simultaneously or subsequently. If the felt is made with a thickness exceeding 0.05 in., it may be found con- 4 venient to mark one surface during manufacture with a series of grooves or striations to assist it in conforming to the shape of the explosive cartridge, If it is desired to use more than one cartridgein a borehole, the sheath should have 4 open ends. so that the propagation ofthe explosion is not hindered. If desired, the sheathing material may be rolled into the form of a tube before the introduction of the explosive.

,parts of suspension supplied to the machine.

Still higher concentrations of suspended material require the use of apparatus of the continuous rotary filter type.

The invention is illustrated by the following examples in which the parts are given by weight.

Example 1 Materials used:-

7 Parts Bleached sulphite wood pulp board (dry 'weight) 7.5 Solid sodium bicarbonate 94.9

Saturated aqueous solution of sodium bicarbonate 350.0

The wet cellulose fibres (37.5 parts) produced by beating the wood pulp board with water are added to the saturated solution of sodium 101- carbonate and mixed therewith in order to cause further disintegration of the bundles of fibres. The solid sodium bicarbonate is then added, due

allowance having been made for the amount of sodium bicarbonate required to saturate the water in the pulp and provide a suspension of solids in which the proportion of sodium bicarbonate to cellulose fibre is 95:5. The ingredients are stirred with a mechanical stirrer for a period of 3 minutes before transferring them to a cloth or metal screen on which they are allowed to drain. Some of the moisture in the drained product is removed by suction, and the sheet is then passed plosive, previously wrapped in waxed manila pa-' to couching rolls; or alternatively the mass may be placed between the absorbent pads, which are then subjected to pressure in order to expel excess water and promote cohesion of the fibres. the felt is then dried at atmospheric pressure for 16 hours at 40C.

A 6 in. x 1% in. cartridge of Polar Saxonite exper, is wrapped in a sheet (5% in. x 4 in.) of the felt' prepared in the above manner. having a thickness of 0.1 in. and weighing about 30 gm.

' The felt is laid on top of a larger sheet of unwaxed paper, so that the sheath and this outer wrapping are applied together. The ends of the outer wrappings are folded in and the whole is dipped in melted wax.

Example 2 Materials used:-

' *Parts Wet beaten Caima St. L. pulp or kraft pulp containing 5 parts of dry fibre--- 25 Solid sodium bicarbonate 96.6

Saturated aqueous solution of sodium bicarbonate I 400.0 Dextrine 2.5

The felt is manufactured from these materials in a similar manner to that described in Example 1.

A 5% in. x 1 in. cartridge of Polar Saxonite explosive is wrapped in waxed manila paper and v is wrapped in a sheet (5% in. x 12 in.) of the felt and the sheathed explosive is finally wrapped in plain paper.

Example 3 Materials used:--

. Parts Wet beaten Caima St. L. pulp or kraft pulp containing 5 parts of dry fibre.-- 25 Solid sodium bicarbonate 96.6

Saturated aqueous solution of sodium bicarbonate 400.0 Magnesium chloride 1.0

The felt is manufactured from these materials in a similar manner to that described in Example 1.

A 5 in. x i in. cartridge of unwrapped Polar Saxonite explosive is wrapped in a sheet (2 in. x 12 in.) of the felt and the ends are folded to form a complete casing. The whole is-then dipped in melted wax.

Example 4 Materials used:

Parts Wet beaten Caima St. L. pulp or kraft pulp containing 5'parts of dry fibre--- 25 Solid sodium bicarbonate 48.3 Solid sodium chloride 48.3

Saturated solution of sodium bicarbonate 200.0

Saturated solution of sodium chloride 200.0

The felt is manufactured from these materials in a similar manner to that described in Example 1.

Atube. 8 in. in length and of internal diameter 1 in., is rolled from a sheet of the felt of sufficient width to give between two and three thicknesses. One end is folded and crimped and a 5% in. x 1 in. cylinder of Polar Saxonite explosive is inserted. The other end of the sheath is then folded and crimped.

Example 5 This example shows the preparation of a felt on a machine of the Fourdrinier type. 20 lb. of wet kraft pulp containing 3 1b. of dry pulp are mixed with 50 lb. of sodium bicarbonate and- 400 lb. water with good agitation. The suspension is supplied to the distributing device on the machine and flowed on to the travelling screen running at a linear speed of 4 ft. per minute. The screen speed is preferably lower than is customary in paper manufacture. The felt was pressed, detached and further dried for-storage purposes. The thickness of the final sheet was 0.062 in.

I claim:

1. A flexible safety sheathing material for; blasting explosives, said material being characteristically of salt and comprising in sheet form a preponderating proportion of a material consisting of at least one substantially non-deliquescent cooling salt, bonded together by a uniforinly distributed amount of cellulosic fiber, said cellulosic fiber being present in the amount of from 2 to 10% of the total weight of the dry constituents of said sheathing material.

2. Sheathing material as in claim 1 to which a small amount of a non-volatile hygroscopic liquid dampening agent has been added to prevent the hardening of said sheathing material.

3. A blasting explosive cartridge sheathed with the material according to claim 1.

4. The sheathing material of claim 1 in which the cooling salt comprises sodium bicarbonate.

5. A flexible safety sheathing material for blasting explosives, said material being characteristlcally of salt and comprising in sheet form a uniform mixture of cellulosic fiber and a preponderating proportion of a material consisting of at least one cooling salt, together with a small amount of a non-volatile hygroscopic liquid dampening agentto prevent the hardening of said sheathing material, said cellulosic fiber being present in the amount of from 2 to of the total weight of the dry constituents of said 10 sheathing material.

' 6. A safety sheathing material for blasting explosives, said material being characteristically in the character of a sheet of cooling salt, as distinguished from an ignitable base material car- 5 rying a modicum of salt, such sheet of coo salt comprising a thin body of salt felted into a sheet with merely sufiicient cellulosic fiber distributed therethrough to impart coherence and flexibility of the wrapping of blasting explosives.

7. A safety sheathing, material for blasting explosives, said material being characteristically in the character of a sheet of cooling salts as distinguished from an ignitable base material carrying a modicum of salt, said sheet of cooling salts comprising a thin body of at least one substantially non-deiiquescent cooling salt 7 felted into a sheet with merely sufilcient cellulosic fiber distributed therethrough to impart coherence and flexibility to the sheet, whereby to adapt the salt to the wrapping of blasting explosives 8. The sheathing material of claim 7 in which:

the cooling salt comprises sodium bicarbonate.

9. An explosive cartridge comprising a blasting explosive enveloped in a sheathing material of the character of a cooling salt in sheet form, as distinguished from an ignitable base material carrying a modicum of salt, said sheathing masheet, adapting the salt to the 3 terial comprising a thin body of salt felted into a sheet with merely suiilcient cellulosie fiber distributed therethrough to impart coherence and flexibility to the sheet, whereby to adapt the salt to the wrapping of blasting explosives.

10. An explosive cartridge comprising a blasting explosive enveloped in a sheathing material of the character of a cooling salt in sheet form, as distinguished from an ignitable base material carrying a modicum of salt, said sheathing material comprising a thin body of at least one substantially non-deliquescent cooling salt felted into a sheet with merely sufilcient cellulosic fiber distributed therethrough to impart coherence and flexibility to the sheet, whereby to adapt the salt to the wrapping of blasting explosives.

11. The explosive cartridge of claim 10, wherein said cooling salt comprises sodium bicarbonate.

12. The explosive cartridge of claim 10, wherein said sheathing material contains sufilcient non-volatile hy roscopic liquid dampening agent to prevent the hardening of said sheathing material.

- l3. A-safety sheathingmaterial for blasting explosives, said material being characteristically in the characterof a sheet of cooling salts, as

distinguished from an ignitable base material carrylng a modicum of salt, said. sheet of cooling salts comprising a thin body of salt, together with sumcient non-volatile hygroscopic liquid dampening agent to prevent the hardening of said sheathing material, felted into a sheet with merely suillcient cellulosic fiber distributed therethrough to impart coherence and flexibility to the sheet, whereby to adapt the salt to the wrapping o'f blasting explosives;

JAMES BINTON BRUCE FLEMING. 

